[Parse] Fix isEditorPlaceholder checks in the parser

Factor out `Token::isEditorPlaceholder` and make sure we're checking
the token's raw text, ensuring we don't ignore backticks.

include/swift/Parse/Token.h

@@ -266,6 +266,9 @@ public:
     }
   }
 
+  /// True if the token is an editor placeholder.
+  bool isEditorPlaceholder() const;
+
   /// True if the string literal token is multiline.
   bool isMultilineString() const {
     return MultilineString;

lib/Parse/ParseExpr.cpp

@@ -35,6 +35,10 @@
 
 using namespace swift;
 
+bool Token::isEditorPlaceholder() const {
+  return is(tok::identifier) && Identifier::isEditorPlaceholder(getRawText());
+}
+
 /// parseExpr
 ///
 ///   expr:
@@ -2206,7 +2210,7 @@ static bool tryParseArgLabelList(Parser &P, Parser::DeclNameOptions flags,
   // An argument label.
   bool nextIsArgLabel = next.canBeArgumentLabel() || next.is(tok::colon);
   // An editor placeholder.
-  bool nextIsPlaceholder = Identifier::isEditorPlaceholder(next.getText());
+  bool nextIsPlaceholder = next.isEditorPlaceholder();
 
   if (!(nextIsRParen || nextIsArgLabel || nextIsPlaceholder))
     return false;
@@ -2402,7 +2406,7 @@ ParserResult<Expr> Parser::parseExprIdentifier(bool allowKeyword) {
     hasGenericArgumentList = true;
   }
   
-  if (name.getBaseName().isEditorPlaceholder()) {
+  if (IdentTok.isEditorPlaceholder()) {
     return makeParserResult(
         status, parseExprEditorPlaceholder(IdentTok, name.getBaseIdentifier()));
   }
@@ -3301,8 +3305,7 @@ static bool isStartOfLabelledTrailingClosure(Parser &P) {
     return true;
   // Parse editor placeholder as trailing closure so SourceKit can expand it to
   // closure literal.
-  if (P.peekToken().is(tok::identifier) &&
-      Identifier::isEditorPlaceholder(P.peekToken().getText()))
+  if (P.peekToken().isEditorPlaceholder())
     return true;
   // Consider `label: <complete>` that the user is trying to write a closure.
   if (P.peekToken().is(tok::code_complete) && !P.peekToken().isAtStartOfLine())
@@ -3360,8 +3363,8 @@ Parser::parseTrailingClosures(bool isExprBasic, SourceRange calleeRange,
       closure = parseExprClosure();
     } else if (Tok.is(tok::identifier)) {
       // Parse editor placeholder as a closure literal.
-      assert(Identifier::isEditorPlaceholder(Tok.getText()));
-      Identifier name = Context.getIdentifier(Tok.getText());
+      assert(Tok.isEditorPlaceholder());
+      Identifier name = Context.getIdentifier(Tok.getRawText());
       closure = makeParserResult(parseExprEditorPlaceholder(Tok, name));
       consumeToken(tok::identifier);
     } else if (Tok.is(tok::code_complete)) {

test/ASTGen/diagnostics.swift

@@ -21,6 +21,10 @@ func testRegexLiteral() {
 func testEditorPlaceholder() -> Int {
   func foo(_ x: String) {}
   foo(<#T##x: String##String#>) // expected-error {{editor placeholder in source file}})
+
+  // Make sure we don't try to parse this as an editor placeholder.
+  _ = `<#foo#>` // expected-error {{cannot find '<#foo#>' in scope}}
+
   return <#T##Int#> // expected-error {{editor placeholder in source file}}
 }
 
@@ -79,4 +83,4 @@ using @Test
 // expected-error@-1 {{default isolation can only be set to '@MainActor' or 'nonisolated'}}
 
 using test
-// expected-error@-1 {{default isolation can only be set to '@MainActor' or 'nonisolated'}}
+// expected-error@-1 {{default isolation can only be set to '@MainActor' or 'nonisolated'}}

test/Sema/editor_placeholders.swift

@@ -27,6 +27,12 @@ f(<#T#> + 1) // expected-error{{editor placeholder in source file}}
 f(<#T##Int#>) // expected-error{{editor placeholder in source file}}
 f(<#T##String#>) // expected-error{{editor placeholder in source file}} expected-error{{cannot convert value of type 'String' to expected argument type 'Int'}}
 
+<#foo#>(x:)<Int>; // expected-error {{editor placeholder in source file}}
+
+// These are actually raw identifiers
+`<#foo#>` // expected-error {{cannot find '<#foo#>' in scope}}
+`<#foo#>`(x:)<Int>; // expected-error {{cannot find '<#foo#>(x:)' in scope}}
+
 for x in <#T#> { // expected-error{{editor placeholder in source file}} expected-error{{for-in loop requires '()' to conform to 'Sequence'}}
 
 }